1. Field of the Invention
The present invention relates to liquid crystal display (LCD), and more specifically, to a LCD adopting gate driver on array (GOA) substrate.
2. Description of the Prior Art
A gate driver is disposed on a glass substrate comprising a thin film transistor (TFT) in the process of a thin film transistor liquid crystal display (TFT-LCD) array for performing row-by-row scanning.
A GOA circuit comprises a plurality of shift register units, each composed of a pull-up circuit, a pull-up control circuit, a pull-down circuit, a pull-down holding circuit and a boost circuit responsible for boosting the electric potential.
The pull-up circuit mainly outputs an inputted clock signal to a gate of the TFT as a drive signal for the LCD. The pull-up control circuit controls the switching of the pull-up circuit, mostly triggered by a signal transmitted from a previous stage GOA circuit. The pull-down circuit rapidly pulls the electric potential of a scan signal (i.e. the electric potential of the TFT's gate) to a low level after outputting the scan signal. The pull-down holding circuit, two operating alternately in most cases, holds the scan signal and a pull-up circuit signal (i.e. signals imposed on node Q) in an off status (i.e. a designated negative potential). The boost circuit is for two boosts of node Q's electric potential to ensure a normal output of G(n) of the pull-up circuit.
Generally speaking, the voltage of node Q of the shift register unit at the current stage is pulled up by the output voltage of the shift register unit at a previous stage, and is pulled down by the output voltage of the shift register unit at a next stage. Therefore, the GOA circuit needs at least two start signals STV1 and STV2. The start signal STV1 serves as a pull-up signal of node Q for the shift register unit at a first stage. The start signal STV2 serves as a pull-down signal of node Q for the shift register unit at a last stage. However, applying two start signals means more wires are needed to transmit signals, which increases the complexity in design.